Forty professional athletes from 14 countries invited for 117th running of Boston Marathon on Monday, April 15

BOSTON - Reigning champions Wesley Korir and Sharon Cherop, both of Kenya, return to defend their titles at the 117th Boston Marathon, but will be fiercely challenged by a talented international field of Olympians, World Marathon Majors champions of Chicago, New York City and Boston, and multiple global marathon winners, race sponsor John Hancock Financial announced.

Last year Korir and Cherop battled not only one of the strongest fields ever assembled, but also blistering race day temperatures topping 85F. Korir prevailed over countryman Levy Matebo in the final mile and Cherop used past experience to surge on the final turn to win the women's race by two seconds.

Challenging Korir for the coveted laurel wreath this year is a fast group of men including 2011 Boston runner-up and 2011 Chicago champion Moses Mosop of Kenya. Mosop's 2 hour, 3 minute, 6 second Boston performance was the second-fastest time ever run over the marathon distance. Joining him in the chase is two-time Olympian and 2010 New York City winner Gebre Gebremariam of Ethiopia. Gebremariam has experience on the course, finishing third in 2011 in 2:04:53. Matebo has also committed to return to Boston to improve upon his second place finish last year and brings additional credentials as marathon champion in Barcelona and Brussels.

American Ryan Hall, who owns the 2:04:58 U.S. course record in Boston, and countryman Meb Keflezighi, past New York City winner and Olympic silver medalist, will work together to bring back a title for the U.S. Both Hall and Keflezighi have finished as high as third in Boston.

Former Boston champion and former course-record-holder Robert Kiprono Cheruiyot of Kenya also returns to the John Hancock Elite Athlete Team and will be joined by the 2012 Eindhoven course-record-holder Dickson Chumba, also of Kenya. Additional talent from Ethiopia includes 2011 Los Angeles champion and course-record-holder Markos Geneti, 2012 Paris and Mumbai runner-up Raji Assefa and the 2012 Hamburg and 2011 Toronto winner Shami Abdullah Dawit.

Guor Marial from South Sudan is also in the field. Marial was granted refugee status in the U.S. after fleeing Sudan during the Civil War. Eight of his brothers and sisters were killed in the conflict. Marial, now a U.S. resident, went to high school in Concord, New Hampshire, and college at Iowa State. After qualifying for the 2012 Olympics, but not yet having a country to run for, the International Olympic Committee honored him with entry to participate under the Olympic Flag.

Also in contention for the crown are four-time U.S. Olympian Abdi Abdirahman who will make his debut on the Boston course as will Australian Olympian Jeffrey Hunt and Canadians Robin Watson and two-time Olympian Eric Gillis.

Americans Jason Hartmann and Fernando Cabada are also contenders. Hartmann finished fourth last year and Cabada holds the American record in the 25K. Joining them to round out the deep field is half marathon specialist Lucas Rotich of Kenya, who holds a 59:44 half-marathon best and countryman Micah Kogo, a 59:07 half-marathoner, 10,000m Beijing bronze medalist, and former 10K world-record-holder (27:01).

Top Olympians Tetiana Gamera-Shmyrko of the Ukraine and Americans Shalane Flanagan and Kara Goucher will present a strong challenge. Gamera-Shmyrko placed fifth at the London Olympic Marathon and Flanagan and Goucher finished tenth and eleventh respectively. Flanagan is a three-time Olympian, winning the bronze medal in the 10,000m in Beijing, and finished runner-up in her marathon debut in New York City before winning the U.S. Olympic Trials Marathon. Goucher has experience on the Boston course finishing as high as third in 2009 and fifth in 2011.

Also focused on the podium are Mamitu Daska of Ethiopia, who is past champion of Frankfurt, Houston, and Dubai; Alemita Abera Begna of Ethiopia, champion of Houston, Daegu and Istanbul; three-time Olympian Sabrina Mockenhaupt of Germany, champion of Frankfurt and two-time winner of Cologne and two-time Olympian René Kalmer of South Africa, who is the past marathon champion of Soweto and Johannesburg.

The 2013 Boston Marathon marks the 28th year of John Hancock's landmark sponsorship of the race. For additional information about the John Hancock Elite Athlete Team and sponsorship, please visit JohnHancock.com or follow @jhboston26 on Twitter.